1. Field of the Invention
The present invention relates in general to a resistor element having a thin electrically resistive film, and more particularly to such a resistor element which is suitably used for a temperature sensor or a thermal flow meter, for example.
2. Discussion of the Related Art
One example of the resistor element having a thin metallic film as shown in FIG. 1 is proposed by the assignee of the present application, and is disclosed in co-pending application, Ser. No. 07/669,007 filed on Mar. 13, 1991. This resistor element includes a ceramic substrate 2 made of alumina, for example, and a thin metallic film 4 formed in a suitable pattern on one major surface of the substrate 2 so as to have a predetermined resistance value. The metallic film 4 is made of platinum, for example. This metallic film 4 is electrically connected to a pair of lead wires 6, 6, made of platinum, for example, at opposite end portions of the ceramic substrate 2, by an electrically conductive adhesive 8 which is a mixture of an electrically conductive material, such as platinum, and glass. On the upper surface of the ceramic substrate 2 on which the metallic film 4 is formed, there is provided a protective coating layer 10 made of glass, for example, which has a suitable thickness.
In this type of resistor element, end portions of the lead wires 6 are disposed on the metallic film 4 formed on the ceramic substrate 2, and then coated with the electrically conductive adhesive 8 so that the lead wires 6 are electrically connected to the metallic film 4. However, this arrangement unfavorably increases an overall thickness of the resistor element, causing some trouble when the resistor element is installed on various devices, such as a temperature sensor. Further, the resistor element constructed as described above has another drawback. If various external forces act on the lead wires 6 while an electrically conductive paste applied to the metallic film 4 is dried and then heat-treated to form the adhesive 8 in the process of fabricating the resistor element, or while the lead wires 6 are handled during practical use of the element, the conductive adhesive 8 is subjected to stress, and suffers from cracks, resulting from the stress. Thus the conventional resistor element constructed as described above suffers from some problems such as low operating reliability and durability.